1. Field of the Invention
The present invention relates to a directly modulated microwave source for use in communications equipment and more particularly to a microwave source combining an oscillator and an impedance matching section for adjustable coupling to a load.
2. Prior Art
Microwave sources of the type of interest herein find use in communications equipment, where they constitute the principal source of transmitted energy and are subject to direct modulation by an information signal for purposes of communicating information to a remote location. As the term microwave implies, the frequencies contemplated are of short wavelength, and are generally above 1 gigahertz. Actual communications band assignments are in the vicinity of 18 gHz and 22 gHz.
A known high frequency source has been fabricated using rectangular waveguide terminated at one end with a shorting end wall at the other end with an apertured end wall through which energy may be coupled to a load. The aperatured partition is typically at a fixed position in the waveguide and of fixed dimensions. Accordingly, when greater coupling is to be sought a simple means of adjustment is to increase the size of the aperture by boring it out. The method leads to only approximate matching, and is irreversable. In a conventional design a variable impedance transformer following the aperture may be required to insure adequate coupling when the load impedance has a different value from that of the oscillator or changes as the equipment is adjusted.
In practice, it is desirable that such resonators be directly modulatable as by a varactor diode, be sensitive to the modulating signal, be readily tuned to an exact operating frequency, have good frequency stability against temperature variation and yet be of a simple, low cost construction.
Because of the small size of the waveguide element, the four or five adjusting elements must be carefully positioned, to avoid unnecessary electrical interaction, and maximum mechanical convenience.